First, just to put things into perspective, like the treasury bonds they hold, treasury ETFs are regarded as among the most efficient and the safest instruments in the world. One reason for this is the liquidity of the underlying market. The U.S. treasury market is the world's largest. The U.S. has a staggering amount of debt outstanding: $27 trillion, more than half the size of the international debt market, estimated at about $50 trillion.

Experienced investors in biotechnology companies have learned to think like venture capitalists: they spread the risk. This makes biotech-focused ETFs, which are inherently diversified, ideal vehicles for investors in the sector. But which ETF is the best? Although there are currently only four ETFs focused on biotech to choose from, because their holdings tend to be so diverse, ranking these funds is more difficult than many other sub-asset classes. The four funds and their expense ratios follow: